HR: 1400h
AN: V53B-11    [Abstracts]
TI: The Volcanosedimentary and Plutonic Assemblage of the Sierra de Zacatecas, Mexico, an Early Cretaceous Volcanic Field
AU: EscalonaAlcazar, F
EM: felscalona@gmail.com
AF: Instituto de Ecologia y Medio Ambiente de Zacatecas, Av. Hidalgo 604, Col. Centro, Zacatecas, ZAC 98000, Mexico
AU: EscalonaAlcazar, F
EM: felscalona@gmail.com
AF: Division de Ciencias de la Tierra, CICESE, Km 107 carr. Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: EscalonaAlcazar, F
EM: felscalona@gmail.com
AF: Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, Amsterdam, HV 1081, Netherlands
AU: * Delgado-Argote, L A
EM: ldelgado@cicese.mx
AF: Division de Ciencias de la Tierra, CICESE, Km 107 carr. Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Weber, B
EM: bweber@cicese.mx
AF: Division de Ciencias de la Tierra, CICESE, Km 107 carr. Tijuana-Ensenada, Ensenada, BC 22860, Mexico
AU: Valencia, V
EM: victorv@geo.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 East Fourth St, Tucson, AZ 85721- 0077, United States
AU: Nunez-Pena, E P
EM: epnunez@yahoo.com.mx
AF: Unidad de Ciencias de la Tierra, Universidad Autónoma de Zacatecas, Calzada de la Universidad 108, Col. Progreso, Zacatecas, ZAC 98058, Mexico
AU: Ortiz-Acevedo, O
EM: ooa@yahoo.com.mx
AF: Unidad de Ciencias de la Tierra, Universidad Autónoma de Zacatecas, Calzada de la Universidad 108, Col. Progreso, Zacatecas, ZAC 98058, Mexico
AB: Based on fossil evidence, the lowermost stratigraphic unit of the Sierra de Zacatecas (SZ), La Pimienta Fm. (LPF), has been considered as Upper Triassic in age (Carnian-Norian). It is covered by the poorly described Las Pilas Diorite (here named Las Pilas volcanosedimentary sequence -LPVS) of unknown age. In this work we present the results of field work, U-Pb dating of zircons and structural analysis. From these results we propose a new interpretation on the stratigraphy, age and origin of the sequence in the SZ. The LPF is composed of schists and phylites derived from fine grained sandstones interbedded with lenses of limestone, and minor tuffs (?) and lava flows. The whole sequence shows a well developed foliation whose average pole is at 86/235.The top of LPF contains a unit of brecciated blocks of phylites and basalt in a fine- grained matrix that includes plagioclase phenocrystals and sulfides, that presumably is part of a fumarolic mound. U-Pb dated zircons from the metasandstones yield an age interval of 161-132 Ma (peak age is 132 Ma). In a gradual stratigraphic continuity, the LPF is covered by the LPVS, made up by cpx-rich basaltic massive and pillowed lava flows, interbedded with mudstone, feldesphatic wacke, greywacke, and tuffs(?). Up section the sediment content and grain size increase. Intruding the LPVS there are Northwestward trending dikes and sills of dioritic composition; also small semicircular bodies of cpx-diorite. U-Pb ages of detrital zircons from a wacke of the upper part of the LPVS yield an age interval of 141-133 Ma. Foliation and stratification are indistinguishable in the LPVS, whose average pole is at 86/244. The apparent gradual stratigraphic order, the U-Pb ages from detrital zircons, and the similar style of deformation of the LPF and LPVS stratigraphic units strongly suggest the presence of an Early Cretaceous volcanic field that is part of an island arc. Our new results deny the Upper Triassic age for LPF and open a new revision of the Mesozoic tectonic history of central Mexico.
DE: 3642 Intrusive structures and rocks
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly